The present invention relates to an RF probe coil for nuclear magnetic resonance (NMR), and more particularly to a quadrature probe in which two sets of probe coils can be easily made orthogonal to each other.
Conventionally, X-ray computed tomography (CT) or ultrasonic imaging apparatuses have been widely used as apparatuses for non-destructively examining an internal structure such as the head or abdomen of a human body. In recent years, attempts to conduct a similar examination by use of a nuclear magnetic resonance phenomenon have given successful results and it has been found out that information unobtainable in the X-ray CT or ultrasonic imaging apparatuses can be acquired.
In an imaging system utilizing the nuclear magnetic resonance phenomenon, the improvement of efficiency of a probe coil for generating or receiving a high frequency (RF) magnetic field is an important task which brings the improvement of image quality and/or the reduction of a time required for imaging. As one approach for solving such a task has been proposed a quadrature probe coil by Journal of Magnetic Resonance, Vol. 69 (1987), pp. 236-242. In the proposed quadrature probe coil, four pieces of outer conductors and two pieces of inner conductors called guard rings are coupled to each other through a dielectric bobbin to form two sets of high frequency (RF) coils which are orthogonal to each other. When the directions of the center axes of the two sets of coils are accurately orthogonal to each other, any interference between the two sets of coils is eliminated and the probe can operate with a high efficiency. This means that a tolerance for error in fabrication of the probe is small and a long adjustment time is required for attaining the orthogonality between the center axes of the two sets of coils.